WO2011133691A1 - Incorporation de nanoparticules métalliques dans un substrat en bois et procédés afférents - Google Patents

Incorporation de nanoparticules métalliques dans un substrat en bois et procédés afférents Download PDF

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WO2011133691A1
WO2011133691A1 PCT/US2011/033284 US2011033284W WO2011133691A1 WO 2011133691 A1 WO2011133691 A1 WO 2011133691A1 US 2011033284 W US2011033284 W US 2011033284W WO 2011133691 A1 WO2011133691 A1 WO 2011133691A1
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wood
nanoparticles
ionic liquid
substrate
cellulose
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PCT/US2011/033284
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English (en)
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Kirk D. Rector
Marcel Lucas
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Los Alamos National Security, Llc
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Priority to US13/642,060 priority Critical patent/US9174355B2/en
Publication of WO2011133691A1 publication Critical patent/WO2011133691A1/fr

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
    • B27K—PROCESSES, APPARATUS OR SELECTION OF SUBSTANCES FOR IMPREGNATING, STAINING, DYEING, BLEACHING OF WOOD OR SIMILAR MATERIALS, OR TREATING OF WOOD OR SIMILAR MATERIALS WITH PERMEANT LIQUIDS, NOT OTHERWISE PROVIDED FOR; CHEMICAL OR PHYSICAL TREATMENT OF CORK, CANE, REED, STRAW OR SIMILAR MATERIALS
    • B27K3/00—Impregnating wood, e.g. impregnation pretreatment, for example puncturing; Wood impregnation aids not directly involved in the impregnation process
    • B27K3/007—Impregnating wood, e.g. impregnation pretreatment, for example puncturing; Wood impregnation aids not directly involved in the impregnation process employing compositions comprising nanoparticles
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
    • D21H17/63—Inorganic compounds
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/65—Raman scattering
    • G01N21/658—Raman scattering enhancement Raman, e.g. surface plasmons
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/46—Wood
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/48—Biological material, e.g. blood, urine; Haemocytometers
    • G01N33/50—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing
    • G01N33/53—Immunoassay; Biospecific binding assay; Materials therefor
    • G01N33/543—Immunoassay; Biospecific binding assay; Materials therefor with an insoluble carrier for immobilising immunochemicals
    • G01N33/54366—Apparatus specially adapted for solid-phase testing
    • G01N33/54373—Apparatus specially adapted for solid-phase testing involving physiochemical end-point determination, e.g. wave-guides, FETS, gratings
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/48—Biological material, e.g. blood, urine; Haemocytometers
    • G01N33/50—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing
    • G01N33/58—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing involving labelled substances
    • G01N33/585—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing involving labelled substances with a particulate label, e.g. coloured latex
    • G01N33/587—Nanoparticles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
    • B27K—PROCESSES, APPARATUS OR SELECTION OF SUBSTANCES FOR IMPREGNATING, STAINING, DYEING, BLEACHING OF WOOD OR SIMILAR MATERIALS, OR TREATING OF WOOD OR SIMILAR MATERIALS WITH PERMEANT LIQUIDS, NOT OTHERWISE PROVIDED FOR; CHEMICAL OR PHYSICAL TREATMENT OF CORK, CANE, REED, STRAW OR SIMILAR MATERIALS
    • B27K3/00—Impregnating wood, e.g. impregnation pretreatment, for example puncturing; Wood impregnation aids not directly involved in the impregnation process
    • B27K3/02—Processes; Apparatus
    • B27K3/0207—Pretreatment of wood before impregnation
    • B27K3/0221—Pore opening
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
    • B27K—PROCESSES, APPARATUS OR SELECTION OF SUBSTANCES FOR IMPREGNATING, STAINING, DYEING, BLEACHING OF WOOD OR SIMILAR MATERIALS, OR TREATING OF WOOD OR SIMILAR MATERIALS WITH PERMEANT LIQUIDS, NOT OTHERWISE PROVIDED FOR; CHEMICAL OR PHYSICAL TREATMENT OF CORK, CANE, REED, STRAW OR SIMILAR MATERIALS
    • B27K3/00—Impregnating wood, e.g. impregnation pretreatment, for example puncturing; Wood impregnation aids not directly involved in the impregnation process
    • B27K3/16—Inorganic impregnating agents
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/4935—Impregnated naturally solid product [e.g., leather, stone, etc.]
    • Y10T428/662—Wood timber product [e.g., piling, post, veneer, etc.]

Definitions

  • the present invention relates to incorporation of metal nanoparticles into wood substrates, to articles that are wood substrates with incorporated metal particles, to sensing changes in the chemical environment in such articles, and to treating such articles with microwaves.
  • Lignocellulosic biomass is plant biomass that is composed of cellulose, hemicellulose, and lignin. Cellulose and hemicellulose are carbohydrate polymers that are tightly bound to the lignin. Lignocellulosic biomass can be grouped into four main categories: (1) agricultural residues; (2) energy crops; (3) wood residues, including sawmill and paper mill discards; and (4) municipal paper waste. Lignocellulosic biomass represents a potentially sustainable source of fuel and commodity chemicals, offers economic advantages over corn starch for the production of biofuels, and could contribute to carbon sequestration without impacting food crop prices [1]. Lignocellulosic biomass could satisfy the energy needs for transportation and electricity generation, while contributing to carbon sequestration and limiting the accumulation of greenhouse gases in the atmosphere.
  • lignocellulosic biomass are abundant and include crops (e.g. corn and sugarcane), agricultural wastes, forest products (e.g. wood), grasses, and algae.
  • crops e.g. corn and sugarcane
  • agricultural wastes e.g. corn and sugarcane
  • forest products e.g. wood
  • grasses e.g. wood
  • algae e.g. a mamiy or cenuiose, nemiceimiose, ana ngnin.
  • Lignin is an amorphous network of crosslmked phenylpropanoid units.
  • the conversion of lignocellulosic biomass into liquid fuels and/or other commodity chemicals typically includes the following steps: (1) pretreatment; (2) hydrolysis of cellulose and hemicellulose into fermentable sugars; and (3) fermentation of the sugars into the liquid fuels (e.g. ethanol) and other commodity chemicals.
  • the pretreatment is energy-intensive, but necessary due to the complex structure of the plant cell wall and the chemical resistance of lignin, which limits the access of enzymes to cellulose.
  • An ideal pretreatment should break the lignocellulosic complex, increase the active surface area, and decrease the cellulosic crystallinity while limiting the generation of inhibitory by-products and minimizing hazardous wastes and wastewater.
  • pretreatment delignification process that provides enzymes access to cellulose, the main source of fermentable sugars.
  • Most current pretreatments such as ammonia fiber explosion, alkaline hydrolysis, and acid hydrolysis, require high temperatures that increase the operation costs and generate toxic byproducts [2, 3].
  • the pretreatment is also the most expensive step in the conversion of lignocellulosic biomass to ethanol. Less expensive pretreatments that are environmentally friendly are desirable.
  • Ionic liquids are molten salts with melting points at or below a temperature of 100°C. They are characterized by their high conductivity, high density, high thermal conductivity, high thermal stability, and extremely low vapor pressure.
  • Alternative pretreatments involving ionic liquids have been investigated because ionic liquids can dissolve in a few hours various native biomasses that include corn stalk [4, 5], rice straw [4, 5], pine [4, 5, 6, 7, 8], oak [6, 7], spruce [8, 9, 10], maple [11], switchgrass [12], and poplar [7].
  • ionic liquids can dissolve cellulose, lignin, native switchgrass, and wood sawdust ground from spruce, pine, and oak.
  • ionic liquids can be recycled at high yields for further use.
  • Most of these reported studies in ionic liquids were conducted at high temperatures on a conventional heating plate.
  • cellulose-rich wood extracts are precipitated and filtered out.
  • the lignin and other extracts are removed with multiple washings and solvent evaporation.
  • Regenerated cellulose from an ionic liquid solution of wood may have a micro Dial ceimiases remain active at an ionic liquid concentration oi aoout ju o.
  • Microwave irradiation has been increasingly used in chemistry to reduce reaction times from several hours to less than a minute in some cases [16]. It was also applied to the pyrolysis of pine wood pellets [17]. Most studies were conducted in commercial microwave ovens [4, 6, 18], with a few in microwave cavities [17] at a frequency of 2.45 GHz. In contrast to
  • microwave irradiation offers several advantages, including volumetric heating and quick coupling with molecules in the sample, that lead to enhanced energy efficiency [17]. It heats materials through two main mechanisms: dielectric loss in dipolar polarization and friction during ionic conduction [16].
  • Dry wood has a low dielectric loss factor at temperatures up to 500°C, making it a poor microwave absorber [17].
  • the addition of water, a strong microwave absorber at 2.45 GHz, to wood improves the conversion of microwaves into heat [17].
  • Microwaves have been recently used to accelerate the dissolution of wood in ionic liquids [4, 6, 18] and acids [19] with pulses as short as a few seconds, Ionic liquids are excellent microwave absorbers because they are polar and ionic in nature [16, 20].
  • the use of microwave pretreatment (60 x 3 s pulses) before conventional heating reduced the time it takes to completely dissolve pine sawdust in l-ethyl-3-methylimidazolium acetate (EMIMAc) by a factor of about three [6].
  • microwave irradiation increased significantly the yield of 5- hydroxymethylfurfural and furfural produced from the dissolution of pine wood in l-butyl-3- methylimidazole chloride, while reducing the reaction time from 60 min (conventional heating with oil bath at 100°C) to 3 min [4].
  • the biomass was completely immersed in ionic liquid and the dissolution products had to be separated from the ionic liquid, which requires additional energy and water use.
  • their recycling is essential for the economic viability of an up-scaled process [21].
  • [uuijj ine presenx invention inciuaes a wooa amcie comprising wooa ana nanoparticles incorporated into cell walls in the wood, wherein the nanoparticles comprise an elemental metal.
  • the present invention also includes a method for studying wood.
  • the method involves exposing a wood substrate having cell walls to an ionic liquid that is a molten salt that has a melting temperature at or below a temperature of 100°C to induce swelling in the wood, then exposing the swollen wood to an aqueous suspension of nanoparticles, the nanoparticles having surfaces, whereby at least some of the nanoparticles become incorporated into the cell walls, whereby the nanoparticles comprise an elemental metal or metal oxide, and thereafter performing a technique on the wood substrate with nanoparticles incorporated therein selected from surface enhanced Raman microscopy and surface enhanced Raman spectroscopy, wherein said nanoparticles behave a contrast agent for studying the wood.
  • the present invention also includes a sensor capable of responding to changes in the concentration of an analyte in a wood substrate, comprising: a wood substrate comprising cell walls, nanoparticles deposited in the cell walls in the wood substrate, wherein the nanoparticles comprise a metal selected from gold, silver, and copper, said nanoparticles further comprising surfaces, and ligands attached to the surfaces of the nanoparticles, wherein the nanoparticles with attached ligands are capable of responding to changes in the concentration of an analyte in the wood substrate.
  • a sensor capable of responding to changes in the concentration of an analyte in a wood substrate, comprising: a wood substrate comprising cell walls, nanoparticles deposited in the cell walls in the wood substrate, wherein the nanoparticles comprise a metal selected from gold, silver, and copper, said nanoparticles further comprising surfaces, and ligands attached to the surfaces of the nanoparticles, wherein the nanoparticles with attached ligands are capable of responding to changes
  • nanoparticles When nanoparticles are attached with ligands (for example 4-mercaptopyridine), they sense the ligands and how the ligands respond to the chemical environment (e.g. to changes in the concentration of various analytes including but not limited to hydrogen ions, metal ions, gases, liquids, and the like). The wood can then be subjective to a pretreatment or mechanistic study utilizing the modified wood as the substrate.
  • ligands for example 4-mercaptopyridine
  • the invention also includes a method for post-harvest modification of wood or cellulose- based paper, comprising: providing a substrate having a structure that comprises cell walls, the substrate being selected from wood and cellulose-based paper, and incorporating isotopically- enriched cellulose crystals into the cell wall structure.
  • the present invention also includes a method for studying wood, comprising: providing a substrate having a structure that comprises cell walls, the substrate being selected from wood and sirucTure, ana suojecrmg uie wooa ⁇ a pretreatmeni or mecnanisiic siuay utilizing tne isotopically-enriched cellulose crystals inside the wood substrate.
  • the present invention also includes a method for treating wood.
  • the method includes exposing wood having cell wails to an ionic liquid that is a molten salt that has a melting temperature at or below a temperature of 100°C to induce swelling in the wood, and thereafter exposing the now swollen wood to an aqueous suspension of nanoparticles whereby at least some of the nanoparticles become deposited into cell walls, wherein the nanoparticles comprise an elemental metal, and thereafter subjecting the wood and metal nanoparticles inside the wood to microwaves.
  • an ionic liquid that is a molten salt that has a melting temperature at or below a temperature of 100°C to induce swelling in the wood
  • exposing the now swollen wood to an aqueous suspension of nanoparticles whereby at least some of the nanoparticles become deposited into cell walls, wherein the nanoparticles comprise an elemental metal, and thereafter subjecting the wood and metal nanoparticles inside the wood to microwaves.
  • the present invention is concerned with an article of pretreated wood containing metal nanoparticles deposited into cell walls in the wood.
  • the invention is also concerned with a method of pretreating the wood.
  • the pretreatment involves incorporating metal nanoparticles in the wood.
  • the pretreatment involves swelling the wood using an ionic liquid.
  • the ionic liquid is a molten salt having a melting temperature equal to or below 100°C.
  • the method of this invention may be applied to any kind of wood or paper products. Poplar was selected merely to show how the method may be performed. Any other type of wood may be used instead of poplar.
  • a non-limiting list of wood that may be used includes cedar, pine, mahogany, oak, cherry, ash, maple, birch, teak, cocobolo, walnut, the like.
  • the method ot the invention can also be applied to the treatment ot other feedstocks such as corn stovers, rice straw, wheat straw, switchgrass and municipal paper waste.
  • the method of the invention can also be applied to the treatment of wood-based products such as paper, construction materials, and cardboard.
  • Iron (average particle size 10-30 nm) and copper (20-40 nm) nanopowder were purchased from Alfa Aesar (Ward Hill, MA).
  • Suspensions of 20 nm silver, 60 nm silver, 40 nm gold, and 100 nm gold nanoparticles were purchased from BB International, Cambridge, United Kingdom.
  • the method of the invention may also be used with an ionic liquid other than l-ethyl-3- methyl-imidazolium acetate that is also a molten salt with a melting temperature at or below 100°C.
  • l-ethyl-3-methyl-imidazolium cation may be combined with other counter ions besides acetate to provide an ionic liquid useful with this invention.
  • Some of these include, but are not limited to, chloride, fluoride, bromide, iodide, nitrate, sulfate, sulfonate, fluoalkylsulfonate, perchlorate, phosphate, silicate, and the like.
  • ionic liquids at least some of which are molten salts at a temperature of or below 100°C are provided by Hagiwara et al. in "Room Temperature Ionic Liquids of Alkylimidazolium Cations and Fluoro anions", J. Fluorine Chem. vol. 105, (2000), pp. 221-227, incorporated by reference herein.
  • Those ionic liquids oe usea wnn u is invention, ⁇ lviccwen et ai. enrmea "Non-Flammable Electrolytes", also incorporated by reference, also provides a variety of ionic liquids that may be used with this invention.
  • molten salts having a melting temperature at or below 100°C may be used with this invention.
  • Some preferred organic cations of molten salts useful with the invention include, but are not limited to, pyridinium, pyridazinium, pyrimidinium, pyrazinium, imidazolium, pyrazolium, thiazolium, oxazolium, and triazolium. Also included are alkyl-substituted analogs of these materials.
  • a preferred list of quaternary ammonium based ionic liquids are those with a melting temperature at or below 100°C that appear in Table 1 of the publication by Sun et al.
  • the invention is also concerned with a method for pretreatment of wood.
  • samples of thin sections of poplar wood were immersed in ionic liquid at room temperature. This exposure caused the samples of wood to swell. Each of the swollen samples was then exposed to an aqueous suspension of metal nanoparticles. The swelling facilitated introduction of the metal nanoparticles into the wood, but exposure to the suspension also resulted in contraction, trapping metal nanoparticles in the cell walls inside the wood.
  • silver nanoparticles and gold particles were incorporated into the wood. These metal particles ranged in size from 20-100 nanometers (nm). Other elemental metals besides gold and silver were used. For example, nanoparticles of elemental iron were also used. Metal oxides nanoparticles were also used. For example, iron oxide nanoparticles were also used.
  • AXIOVERT 200M inverted microscope A 514 nm laser was used as excitation and the fluorescence signal was collected with the Meta detector over a 600-620 nm range with a 63x oil objective (NA 1.4). After a 3-hour immersion, the cell walls became swollen and the cell lumens were reduced (similar behavior has been observed with switchgrass). From cross-sectional area measurements of poplar wood cells, it was found that after the 3 hour pretreatment, the cell wall areas increased by 60% to 100% and the lumen areas were reduced by 40% to 83%, depending me almost liimieuiaie reopening or me lumen, i ne ceil wans aiso contracted arcer nnsing wim water, but more slowly. By contrast, the deposition of deionized water droplets on untreated poplar wood resulted only in a limited expansion of the wood, and the wood cells recovered their original sizes within 30 minutes after the water evaporated.
  • Nanoparticles of any suitable metal may be used. Nanoparticles of transition metals may be used. Nanoparticles of alkaline earth metals may be used. Nanoparticles of main group metals may be used. Nanoparticles of iron, tin, cobalt, titanium, niobium, tantalum, chromium, molybdenum, tungsten, nickel, copper, and the like, including mixtures and alloys of these materials, may be used.
  • a preferred embodiment involves nanoparticles of elemental gold or silver to serve and contrast and sensing agents in wood.
  • Another preferred embodiment involves nanoparticles of elemental iron, in particular when microwaves are used with iron nanoparticle- incorporated wood.
  • Nanoparticles have a high surface-to- volume ratio and may be chemically functionalized.
  • Some potential applications of the method, which involves swelling of the wood using the ionic liquid, include isotope tracing, catalysis, imaging agents, drug-delivery systems, energy storage devices, and chemical sensors.
  • incorporation of material may be due to an affinity of the material to the substrate and the size of the cell wall structures, which typically are 2-3 micrometers in thickness, and thus the interface are potenuany aDie to oe incorporated into ceil wans, ana possioie Digger materials witn sizes less than 50 micrometers may be incorporated into paper. Any elemental materials, charged or neutral and in any oxidation state, in this size range, as well as inorganic oxide, sulfides, or halide-based materials, may be incorporated into the cell walls. Organic-based materials, such as polymers, proteins, and nucleic acid based if they are small enough to enter the cell walls by diffusion.
  • the incorporation of materials into wood or paper products may provide nanoparticle- based sensors useful for measurement of chemical environment, for the presence of specific materials, for quantification of an amount of a chemical present, and the like.
  • Both liquid-based detection and gaseous based detection using metal nanoparticles could be adapted to be incorporated into wood or paper using this invention.
  • SERS-based nanosensors see for example US Nonprovisional application number 12/534,612 to Rector et al. entitled "Surface-enhanced Raman Scattering (SERS) Based Nanoparticle Composites," incorporated by reference, with both a sensing and targeting function for live cellular analyses.
  • palladium nanoparticles can be used to sense gaseous H 2 .
  • Properties of paper which may improve upon existing sensing technology include, low cost, organic-based liquid and gas permeable, and thermally and electrically isolating.
  • isotopic enrichment such as 13 C labeling
  • the excitation for the Raman work was the 776 nm laser line of a tunable Ti:Sapphire laser (MIRA 900-P, COHERENT, Palo Alto, CA) coupled with a 532 solid state laser
  • the Raman signal was collected in a backscattering configuration through the same objective and dichroic.
  • the signal was focused with a 150 mm spherical lens onto a 50 micrometer wide slit at the entrance of a HOLOSPEC f/2.2 spectrograph (KAISER OPTICAL SYSTEMS, Ann Arbor, MI) and filtered with a HOLOGRAPHIC SUPERNOTCH-PLUS filter (HSPF-785.0AR-2.0, KAISER OPTICAL SYSTEMS, Ann Arbor, MI).
  • the signal was then dispersed with a holographic grating (HSG-785-LF, KAISER) and imaged with a liquid nitrogen-cooled CCD camera (LN/CCD-1024E, PRINCETON INSTRUMENTS, Trenton, NJ).
  • the CCD camera recorded spectral information along the horizontal direction and spatial information along the vertical direction.
  • the spectrometer was calibrated spectrally with 4- acetamidophenol, and spatially using lines in the 7 th group of a USAF-1951 resolution test target.
  • Custom-written LAB VIEW code enabled the acquisition of images and their correction for CCD bias voltage, spherical aberrations using the lines of a Kr lamp (NEWPORT CORP, Irvine, CA), and for the non-uniform power along the focused laser line using a NIST relative Raman intensity correction standard (NIST SRM 2241).
  • the Raman images were acquired by moving the sample across the laser line by 0.5 micrometer steps. The exposure time for each line was two minutes.
  • Each CCD image corresponds to the signal from a line on the sample, and consists of 256 spectra collected at regular spatial intervals along that line. Each spectrum was integrated from 1050 cm "1 to 1140 DacKgrouna rrom me sample was removea rrom me aaxa.
  • hot spots in surface enhanced Raman scattering experiments refers to significantly higher than average enhancement of the Raman signal intensity, and is usually believed to arise from specific atomic and nanometer level structures on the surface or from multiple surfaces such as particles aggregating together).
  • To normalize the intensity depth profile of each spot its minimum value was subtracted from it and it was then divided by its maximum value. The error bars represent the uncertainty on the position of the selected 2 x 2 micrometer squared area around the hot spot.
  • samples of wood were treated first with ionic liquid and then with a suspension of metal nanoparticles. After rinsing with water, images of the wood were obtained using scanning electron microscopy (SEM) and Raman spectroscopy to examine the effects of rinsing on the removal of nanoparticles from the wood. The images were of the same areas of the wood. Scanning electron micrographs were acquired using a FEI QUANTA 200FEG operating at an accelerating voltage of 30 kV with a backscatter detector. Samples were mounted on one of the glass cover slips used during Raman imaging.
  • SEM scanning electron microscopy
  • Raman spectroscopy Raman spectroscopy
  • Control experiments were also performed on samples of poplar wood. The control experiments did not involve exposure of the wood to the ionic liquid. Without this exposure, the swelling of the wood from water was greatly less. When these samples were then exposed to the uic uuici suiia e ui uic wuuu. i ncsc iiaiioparucies were easily remuveu uy raising.
  • An ED AX EAGLE III energy dispersive X-ray fluorescence (XRF) microscope was used to quantify nanoparticle uptake by averaging fluorescence over areas of diameter 40-160 micrometers.
  • the instrument includes a rhodium (Rh) source.
  • Settings of 40 kV accelerating voltage, 800 microamperes current, and 50 microseconds dwell time were used to sample the poplar wood sections. In this configuration, only elements with atomic numbers greater than 11 (Na) are detected.
  • Na atomic numbers greater than 11
  • several elements are present including S, , Ca, P, and Mn. The presence of elements S, K. Ca, P, and Mn has been reported in Aspen ash. The calcium content was heterogeneous.
  • the signal from phosphorus was weak, but detectable. sections oeiween glass siiaes ciunng arying. m auumon, ⁇ r, re, ⁇ , were ueiecieu, ii eiy present as residue particulates from the microtome blade. In a comparison of total count mapping and elemental mapping, it was determined that K, Mn, and S are the most closely related to both the density and mass of the poplar sample and appear to be homogeneous with material thickness or density. Sulfur concentration (2.30 keV) was selected as an indicator of poplar density as it is most isolated from other spectral signatures.
  • the poplar sample was exposed to the silver suspension for one or four hours without the ionic liquid pretreatment, and rinsed to test for the possibility of silver mechanical or electrostatic association.
  • the XRF measurements indicated that silver was present in the control samples at the detection limit of the instrument. Slightly more silver was present iiquiu anu tiic siivei sus eiisiuxi icsuncu in m icasi ail uiuci ui iiiagiinuuue increase in uic pamuie incorporation.
  • the data suggest that exposure to the ionic liquid or silver suspension longer than 1 hour has only a minor influence on particle incorporation. Further, increased exposure to silver has a negligible or minor influence on particle incorporation on these timescales.
  • the enhancement which reaches two orders of magnitude for some hot spots, indicates that the laser excitation energy is close to the surface plasmon resonance of these nanoparticles of 100 nm diameter, or clusters of these nanoparticles.
  • no noticeable enhancement was observed from 20 nm diameter silver nanoparticles deposited on wood, while only a small enhancement was observed for 60 nm silver and 40 nm gold nanoparticles. Therefore, only the 100 nm gold nanoparticles will be dealt with in the following discussion.
  • Raman images were obtained by integrating Raman spectra from 1050 cm “1 to 1140 cm “1 , a band that includes the cellulose peaks typically located at approximately 1095 cm “1 and 1120 cm “1 in spontaneous Raman spectra (not enhanced by gold nanoparticles). These two cellulose bands are enhanced by a variable factor depending on the hot spot. Also, the 1095 cm “1 band can be shifted to another position from 1081 cm “1 to 1099 cm “1 , while the position of the 1120 cm “ band varies from 1115 cm “1 to 1128 cm “ . The lignin peak at approximately 1600 cm " was not integrated because it overlapped with background signals from the ionic liquid and the glass substrate.
  • Raman images show that the density of hot spots on the untreated sample is comparable to the one on the pretreated sample.
  • the intensity of the hot spots was higher on the pretreated sample. This is partially explained by an overlap between the cellulose and the ionic liquid Raman bands.
  • Kaman images ax the same areas were collected after rinsing for direct comparison. Most hot spots on the untreated sample disappeared after rinsing, leaving only a few for each image covering an area of 35 x 55 micrometers squared.
  • the rinsed sample pretreated with ionic liquid retained most hot spots on the Raman image.
  • nanoparticles and aggregates of nanoparticles observed by SEM yielded a hot spot with variable enhancement on their corresponding Raman images, especially for the pretreated sample with the largest aggregates.
  • the untreated sample with the smaller aggregates a large number of isolated nanoparticles and small aggregates yield no hot spot on the Raman image.
  • the larger aggregate size in the pretreated sample explains the higher intensity of the hot spots, as aggregate size affects the appearance of hot spots and the nanoparticle surface plasmon resonance.
  • the intensity decrease of all hot spots in the pretreated sample after rinsing can be explained by a reduction in aggregate size. This intensity decrease might also be due to removal of some ionic liquid during the rinsing.
  • the Raman and SEM images showed no preferential deposition of nanoparticles in the cell corners, middle lamella, or secondary cell walls.
  • the intensity of six and twelve hot spots was measured as a function of depth for the untreated sample and pretreated sample, respectively. Included were all hot spots that could be tracked across the images at different depths. A few hot spots were excluded because their intensity depth profiles exhibit two distinct maxima. A few large aggregates contained nanoparticles stacked on top of others, and so it was unclear if the maxima correspond to hot spots from the same nanoparticles or multiple nanoparticles.
  • the intensity depth profiles have full width at half maximum ranging from 2 micrometers for the most intense hot spots to 4 micrometers for the less intense hot spots. The depth resolution was sufficient to determine whether the particle is at the surface or incorporated inside the sample.
  • the intensity of all hot spots reached a maximum at depth of approximately 0 micrometers or at a negative depth.
  • the area under the curve for all depth profiles is dominated by contributions from negative depths.
  • the electromagnetic field enhancement around the nanoparticles leading to SERS activity is local, only noticeable within a distance of 10 nm from the nanoparticles. Therefore, the nanoparticles producing these hot spots are all at the surface of the sample.
  • the method of this invention may be applied at room temperature, providing a large cost savings in processing lignocellulosic biomass into fuel and other chemicals.
  • the method of this invention may be applied in a temperature range from about 10°C to about 50°C. Room temperature (approximately 25°C) is preferable because the sample need not be heated or cooled.
  • Microwaves are among the least expensive forms of energy amongst electromagnetic radiation to deliver electromagnetic radiation to a substance. Microwaves also have an ability to penetrate deeply within a large sample of a material. The microwaves may induce dielectric breakdown among the nanoparticles in the wood. The arcing between the particles creates damage to the cell wall structure and may provide a cost effective method to create sites of attack for enzymes and/or other chemicals for breaking down the lignocellulosic biomass. ouiiic exam les ⁇ iecnmqu.es useiui ior separating inese iianoparucies liieiuue, DUL are noi limited to, including filtration and centrifugation. Magnetic separation is also possible when the metal nanoparticle used with the invention includes, for example, an electrically conductive shell and a magnetic core.
  • incorporation of these nanoparticles followed by exposure to microwaves is believed to improve access of enzymes to cellulose.
  • the ionic liquid causes swelling of the wood to an extent that allows incorporation of metal nanoparticles into the wood, which is subsequently treated with microwaves.
  • This incorporation process involving ionic liquids was used to incorporate various metallic and metallic oxides nanoparticles into the wood structure at room temperature.
  • Fe was proven to be an excellent microwave absorber [23, 24] that can convert microwave irradiation into heat transferable to the surrounding wood structure.
  • the evolution of the structure of poplar sections after microwave irradiation was monitored by optical microscopy for samples pretreated with ionic liquid l-ethyl-3-methyl-imidazolium acetate (EMIMAc) with or without embedded metallic and metallic oxides nanoparticles.
  • EMIMAc ionic liquid l-ethyl-3-methyl-imidazolium acetate
  • the ionic liquid is needed during the pretreatment and the incorporation of nanoparticles at room temperature.
  • the ionic liquid could be separated from the nanop article-incorporated wood by a simple filtration.
  • Concentrated suspensions of Fe 2 0 3 , Fe 3 0 4 , Fe and Cu nanoparticles were prepared by immersing 100 mg of nanopowder in 1 mL of deionized water without any surfactant in an argon suspensions were aguaiea witn a vorrex mixer JUST, oeiore rneir aeposmon oi popiar samples.
  • Pretreated poplar samples were first immersed in EMIMAc for 3 hours before the nanoparticle incorporation [22] . After the pretreatment, the excess EMIMAc was blotted with a KIMWIPE. One sample was then immersed in 40 ⁇ , of concentrated suspension and three others in 20 ⁇ of dilute suspension. A second set of four samples was prepared without the EMIMAc
  • a third set of three samples was only pretreated with EMIMAc for 3 hours.
  • a fourth set of three samples was pretreated with EMIMAc and then rinsed with deionized water.
  • a fifth set of three samples was simply rinsed with deionized water. The samples were left to dry for 1 hour in air before microwave irradiation.
  • the pretreated wood sections were placed on a glass slide.
  • a commercial microwave oven (SHARP Carousel R-230K) was used to heat the wood samples. It was operated at the maximum power of 800 W at 2.45 GHz.
  • Optical images were collected from the samples treated with Fe nanopowder using a LEXT OLS4000 measuring laser confocal microscope (Olympus America Inc., Center Valley, PA) equipped with a 20x and a 50x objective. The microscope operates with a 405 run excitation laser. Optical images at different magnifications with spatial coordinates from the microscope stage ensured that the same areas were imaged before the nanoparticle deposition and after microwave irradiation. [0068] Nanoparticles of Fe, Cu, Fe 2 03, and Fe 3 0 4 were incorporated into the poplar cell structure after a pretreatment with EMIMAc.
  • Samples prepared without EMIMAc pretreatment were also exposed to the concentrated and dilute Fe nanoparticle suspension, and heated for the same duration.
  • the sample prepared with the concentrated suspension was also vaporized after 3 min irradiation, with the
  • the first was a mixture of untreated sawdust and Fe nanoparticles in water
  • the second was pretreated with EM IMAc then immersed in water
  • the third was pretreated with EMIMAc and incorporated with Fe nanoparticles in water. All three samples were exposed to three microwave pulses of 10 s. After microwave irradiation, no change in color or boiling was observed in the first sample, despite a moderate rise in temperature, which is consistent with the results from the poplar section.
  • the second sample pretreated without nanoparticles, most of the water was evaporated after vigorous boiling, leaving most sawdust on the tube walls. No significant color change was observed after three pulses of 10 seconds (s).
  • the Fe nanoparticles formed aggregates of sizes ranging from less than a micron to a few tens of microns. The density of particles was mostly uniform across the incorporated sample. Most particles turned red after irradiation, indicating oxidation.
  • the sample with Fe nanoparticles was found after microwave irradiation with the poplar secondary cell walls significantly swollen. The swelling is reminiscent of the swelling observed during EMIMAc pretreatment before water rinsing [22,25], suggesting the presence of residual EMIMAc in the wood sample after rinsing. During swelling, the middle lamellae between cells remained smooth and straight [22].
  • nanoparticles accompanied by the quick thinning of the poplar cell walls also may indicate that a significant amount of cellulose is lost in the form of water, volatiles and C0 2 during the microwave heating [37,38].
  • No noticeable liquid product was found on the underlying glass slide after microwave irradiation. The amount of sugars lost is difficult to measure due to an unknown amount of residual EMIMAc in the pretreated wood.
  • the irradiation time for the poplar sections was longer than those reported in the literature, from multiple pulses of a few seconds [6,18] to 2 min [4]. However, in these previous studies, the samples (pulp or small chips) were completely immersed in ionic liquids.
  • the present invention is more particularly described in the embodiments above, which are intended as illustrative only, since numerous modifications and variations will be apparent to those skilled in the art.
  • the invention may be applicable for incorporating materials/chemicals into wood and paper products, enabling isotope tracing, development of new pretreatments, sensing and imaging capabilities.

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Abstract

Selon l'invention, des nanoparticules métalliques ont été incorporées dans du bois. Des liquides ioniques ont été utilisés pour dilater la structure des parois alvéolaires du bois et y incorporer les nanoparticules. Les nanoparticules d'or ou d'argent élémentaire se sont avérées être des agents de contraste et de détection efficaces en imagerie par spectroscopie Raman exaltée en surface (SERS). Les nanoparticules en fer élémentaire se sont avérées être des absorbeurs de micro-ondes efficaces et ont provoqué un échauffement localisé pour rompre l'intégrité de la matrice lignocellulosique. Des échantillons témoins suggèrent que l'échauffement localisé autour des nanoparticules en fer réduit les pertes de cellulose sous forme d'eau, de composés volatils et de CO2. Le liquide ionique est nécessaire pendant le procédé d'incorporation à température ambiante. L'utilisation de petites quantités de liquide ionique, combinée à l'absence d'étape de purification dudit liquide ionique et à une utilisation moindre d'énergie et d'eau, devrait permettre de réduire les coûts dans un procédé de prétraitement à plus grande échelle.
PCT/US2011/033284 2010-04-20 2011-04-20 Incorporation de nanoparticules métalliques dans un substrat en bois et procédés afférents WO2011133691A1 (fr)

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